Art of stiffening



COMPOSITIONS, COATING OR PLASTIC.

I ,so

UNITED STATES PATENT OFFICE WILLIS A.

00., OF BOSTON,

BOUG KTOH, O! GAIBBIDGE, IABSACHUSETTB, ABSIGNOB TO BENNETT BOX MASSACHUSETTS, A. CORPORATION OF MASSACHUSETTS LIB-'1 OF STIFFDTING Ho Drawing.

This invention relates to improvements in the art of stiffening. More especially it relates to improvements in processes by which sheet materials of industrial utility, such as cloth, leather or paper may be made stiffer than they are by nature. It is especially useful for various articles of manufacture such as hat shapes, counters of shoes, and kindred fabrications, including box toes of shoes. It belongs to the general class in which material is applied in liquid form at ordinary temperatures, and the stiffening results from atmospheric drying.

In the manfacture of toe boxes, for which the invention has important utility, it is particularly desirable to provide so that the box can be bent in by pressure but will immediately resume its original form when the pressure is removed. It is one object of the invention to rovide such a box.

he invention also combines certain advantageous industrial characteristics which have long been sought in the general art to which the invention relates. Amon these are that the materials employed shoufi be inherently inexpensive, and should be easily obtainable in abundant quantities and standard quality. Another is, that the result of the treatment should be permanent,'the material maintaining whatever degree of stiffness it acquires, or imparts, without being easily affected by moisture, as are lues; nor by heat, as are waxes, asphalts, pitches and shellacs. Others are that it should be non-putrescible; should be odorless, and remain so when heated or wetted; should not injuriously affect the sheet materials with which it is used, nor alter their properties within a. reasonable length of time, nor deface them, as when a black or colored waxy or pitchy stiffener sometimes permeates to and discolors the face of a white shoe leather. It should be safe when handled and stored in quantities in the factory and should not entail the storage or handling of an y dangerous substance for the working of it, as does celluloid, for example. It should moreover be easy to handle in the factory; and should produce the desired stiffness With. sufiicien! rapidity. Furthermore it is desirable to be able to predetermine the degree of StIfiDGS:

Application fled December 15, 1822. lcrlal No. 607,218.

which the box shall have, because sometimes a marked degree of fiexibilit is desired and for other purposes a practice ly unyielding box is desired. The resent invention attains all of these standar s, and in so doing combines in itself characteristic advantages that have never heretofore, so far as I am aware, been associated in any practicable stiffening process or stifi'ened product.

In the best form in which I at present contemplate using it these objects are attained by applying a substance which'is made liquid by the presence of water, but which is capable of conversion to solid form while still containing a very considerable amount of water. The stiflening is accomplished by solidification in the presence of considerable moisture. I have found suitable material for this in the hi h ratio silicates of alkali metals, that is, SlfflCtiIGS contalmng th'ehlii E611; propgrtions o si ica to soda or otas uc ma ecome fdry and hard, tliat is, may acquiri; the aspect and physical effect of substances that are free from moisture, and yet may at the same time contain as much as per cent of water. Under these circumstances, if a proper concentration of the liquid silicate be used, as for example one containing less than 60 per cent of water, the difference between its fluid state, in which it can be conveniently applied to and can penetrate a supporting medium such as felt or aper, and its solid state in which it makes t at medium stiff, means that the drying is accomplished by removal ofonly small percentage of its water content. With other water-soluble stifiening materials, e. g. lues, the difference between water content m liquid state and water content in solid state is usually much more than this. For the purposes ofthe invention sodium silicates having a formula of the order of I\I'a O(SiO or Na Os SiO seem to have mm H1106 es or 0 er arrangement of such size and character that a certain residual quantity of the water is associated with the molecules of the solids far more intimately than ordinary water of solution. When a film of such soum silicate is exposed to evaporative influcc, the material at the surface of the film uickly red d to semi-solid, non-sticky state, in which the material hearing it may be handled conveniently, and from which state its drying continues till the whole becomes a hard, horn mass. I have found these effects present in the said silicates having high ratio of silica to sodium, much more satisfactory than in sodium silicates of lower silica to sodium ratio. The high ratio silicate gives a greater stiffness and strength of film when compared with the equal ratio sodium silicate having the same amount of anhydrous material. The ratio of silica to alkali does not affect the amount of total solids present in any case, but merely the proportion of the two radicals composing any weight of anhydrous material; thus, if there be 40 per cent of anhydrous material present in the two varieties, the Na O and the SiO may in the latter be in equal molecular proportions, and in the former may exist in the ratio of 1 to 4. The water present is variable in amount. It will be understood that the formulas herein given are merely illustrative and do not necessarily convey the exact idea of the way in which the alkali and silica radicals are grouped, or may be supposed to be grouped.

Moreover, although the high ratio silicate solution feels alkaline, it does not act chemically alkalineas do the low ratio sodium silicates. Itdoes not rot cloth and when once dried is less soluble in water and less subject to deterioration. It will be understood that the word soluble is used herein in its popular sense of becoming liquefied on addition of water, without touching the technical question whether a soluble silicate goes actually into true solution or into suspension, or otherwise. In the high ratio sodium silicate micelle or molecule-grouping, the alkali is less firmly attached to the grouping than is the sodium in such a salt as sodium chloride. The approximate balancing of its attachment, or balancing of alkalinity, is a matter of great advantage in the present invention, as compared with other stifl'eners such as glue.

It is sometimes desired to apply a stiffening agent to a sheet with the aid of an auxiliary sheet as a supporting medium. The sodium silicate solution combine-s particularly well with paper felt, untreated roofing felt, blottin felt, and unsized paper matte, bleache or unbleached cotton or woolen felt, or felted or fiannelled surfaces, or even surfaces without nap, as, for exam le, in the manufacture of a box toe. t is recognized as a technically diflicult process to saturate thoroughly sheet materials such as those named with a stiffener such as glue; but the silicate solution of the invention readily soaks into such fibers and fills the res. It is my belief that this action is ue to the fact that radicals of the sodium silicate molecule, in whatever form it exists in these high ratio silicates, sociate suficiently when the chemical co tions call for dissociatnn, to yield a small proportion of free hyrr'oxyl ions; that there is usually more or less grease present on felt of any kind, or cloth; and that the hydroxyl ions which attend the silicate solution are efficient in de-greasing the fiber so thatthe solution readilyenters and may effect both inter-fibrous and intra-fibrous penetration.

As with other stifi'eners, e. g. casein or glue, a silicate stiffenin will absorb a certain amount of water w en exposed to water vapor or liquid; and it is therefore ordinarily desirable to protect such stifi'eners from the action of water. One of the ways in which this may be done is by laying on a coat of waterproofing material, of which suitable types are already in common use. Such a protective coating should form a continuous film. To this end it ma either be applied in a thick and hot condltion, so that when cooled it is approximately solid; or it may be applied as a thin sheet supported on an auxiliary light thin medium such as tissue or other paper. When the waterproofing treatment is applied to a sheet of material which is later to be softened as, for example, for the lasting of a box toe, it is particularly desirable that the waterproofing should be only on the surface, as distinguished from coating each fiber, so as not to prevent the stiffener from taking up enough water to become sufiiciently soft to allow of easy lasting of the box toe.

The contradictory requirements that the stiffening material should be waterproof and yet should be capable of taking up water so as to become soft for the lasting may also become harmonized, according to the invention, by using an auxiliary waterproof layer of material sewed or otherwise permanently or temporarily attached to the underside of the box, which may have been prepared as by skiving. For example, a well known waterproofing material consists of thin stron paper coated with a continuous waterproo ing layer which holds on it a strengthening sheet of coarse mesh cloth. The attachment of this materialto either side of the skived box allows the box to be softened by the action of Wat er on both sides, for the sewed-on material can be held away during dipping, or, if not so, the water can enter at the edges; and yet, when the box has been lasted in the shoe, this material affords a water-proof layer which satisfactorily prevents access through the sheet material of moisture from without, or from perspiration, that might soften the box. Boxes may be built up in any other suitable way, as for example from two or more layers of paper or cloth, to which the silicate solution, acting as adhesive, may attach one side of the water-proof material above described. The whole sheet thus integrated 'nay then be allowed to dry, with or without pressure, and then be cut to shape,

skived if COATlNG R PLASTIC.

COMPOSITlONS,

desired, and wetted? efore lasting, long enough for water to penetrate the un-waterproo ed side sufliciently to allow of easy lastmg. In this case sewing is not necessary as the stiffening material holds the waterproofing material.

The stiffener ma however be waterproofed when there is no such sheet protection. I do this by rendering the surface of the silicate layer in the integrated sheet or stifiened box insoluble, thereby protecting the body of silicate within the stiffened sheet of cloth, paper or felt from attack by the moisture which would soften it if it had access thereto. Such a stiff supporting sheet of felt, etc., can be waterproofed chemically with respect to one or both surfaces, after the sheet has been saturated with silicate and allowed to dry. One method of doing so consists in spraying or painting the surface thereof with an acid solution, or with the solution of a substance which contains free hydrogen ions, or collodion or other substance which will precipitate gelled silica from soluble silicates. By this means a layer of insoluble silica is precipitated on the surface as a body whose physical form is rather similar to that of the sodium silicate solution, in that it is a colloid and occupies considerable volume for the mass of anhydrous material present, but which is not easily soluble in water and which as a film is more continuous because of its colloidal quality than a film made of an ordinary precipitated salt; and which, probably because of its colloidal uality and the diiiiculty with which one co loid passes through another, appears to have a marked and positive effect in preventing the soluble sodium silicate within the said felt or other sheet from dissolving out of it, although at the same time it does not markedly hinder the softening of the sodium silicate within. The depth of the layer of insoluble silica thus formed on the surface of the felt or other medium depends upon the strength of the acid and the length of time of application. Moreover, because the film deposit is a colloid or of a gelatinous nature and occupies considerable volume for the mass of anhydrous material present, there is no marked change in volume, no shrinking or swelling with incidental wrinkles or cracks, resulting from the treatment.

An insoluble coatin for the felt or other material containing the silica solution may also be provided by recipitating an insoluble silicate on the sur ace by treatment with a solution of a solublgsalt which contains an ion of a metal forming an insoluble silicate. Almost any solubl etal salt except those of the alkalies, can be used for t is purpose, such as ma nesium, aluminum, etc.

be applied when the sodiu n silicate is in a gglgjum zinc, The so lition for treating the surface may industrially, gives a great range of freedom as to the time for applying the treatment. It allows material to be prepared, dried, kept dry in storage, and ultimately to be used with or without the waterproofcd surface as may be desired. The degree of concentration of the acid employed may vary. depending on the dryness of the sodium silicate, so as to avoid adding unnecessary water. If the stiffener be still wet the acid may be far more concentrated.

It is another feature of the invention that the qualities of stiffness and flexibility of a stiffened box may be varied in degree, and the brittleness decreased. A supporting medium such as felt. or felted cloth or paper, or cloth sheet, is relatively hard when heavily impregnated with a silicate solution and dried. If it be desired to have a shoe box that is somewhat more flexible, almost any desired degree of flexibility may be obtained by the addition of the requisite amount of glvcerine. soa or soap solution (particularly so-calle' sofi dr in or nond m oil. such as cottons cad Oll or lmseed 011, which can be emulsified with the silicate solution, or any desired combination of these softeners. This may be added to the silicate solution and thoroughly incorporated with that solution,

before impregnating the fibers of 'the said supporting medium.

- By the use of a fatt oil, as above mentioned, advantages of partlcular importance may be attained. I havediscovered that oils of ve etable or animal ori 'n, such as cottond d linseed 01l Wlll emulslfy easlly, rapsee an idly andnompletely vithfsilicatesolution so as to form a mixture which can be applied in every way like the silicate solution and will dry at approximately the same speed or somewhat more slowly. The oils appear to be carried in an extremely finely divided state everywhere that the silicate penetrates and they result in the lubrication of the air dried micelles to such an extent as to produce a springy flexible sheet. A non drying oil, such as cotton seed oil, keeps its 01 y properties and'maintains the flexibility. A d in oil in the emulsion produces a sti s cc w ich takes on the qualities of both silicate stiffness and varnish toughness. In this respect the integrated sheets attain to a marked degree that uality ofspringiness which is much desired for the so-called flexible box toe, and have a comparatively high bending coefficient. That is, they can be bent into a curve which, if a section of a circle, may be of pretty small radius, and may form a comlete circumference, yet when the pressure 1s released they immediately resume practically the original flatness; and in general, vhen bent they snap back with somewhat the iafijgct of a sheet of tempered steel, or of cellu- 5 An advantage of the use of oil emulsion is that the layer of oil around and in the silicate acts markedly as a waterproofing agent. The oil passes liquid water easily to the silicate and so, in the case of a toe box, does not interfere with the softening by liquid for lasting; but such a sheet is less affected by water vapor than are the non-emulsion silicates. This is a feature of importance where it is desired that a box withstand the moisture from perspiration, without having a homogeneous waterproofing layer. Ey including glycerine and oil in theaemllbb a waterproofed sheet may be made of superior resilience, due to the glycerine.

W'ithout employing the foregoing, a somewhat similar effect can be produced by selecting and using for the active stiffening agent a silicate solution containing a smaller proportion of silica to sodium, in which the formation of hydroxyl ions by dissociation gives, in effect, a solution of sodium hydroxide with the sodium ions of the silicate molecules. Caustic alkalies such as sodium hydroxide, being markedly deliquescent, will keep the silicate film from drying to so great a degree. For example, experiment showed that a 1 to 1 ratio solution did not become even surface dry in twenty-four hours. Hence by proper proportioning, almost any desired degree of softness may be attained for a stiffener of material. A similar effect may be produced by the addition of any otner soluble deliquescent salt which does not react chemically with sodium silicate; or, without such addition, by reducing the residual amount of dry stiffening material, as by squeezing out a part immediately after application or by applying it in more dilute form, thus in either case making less dry material in a given volume.

The stiffened product thus far described is inorganic, so far as the stiffening material is concerned, and therefore will not decay or mold. When sutiiciently air dried it is not softened by the action of heat under temgetfatures at which leather itself is injured.

e materials required are low in cost and easily available in large quantities in the market. The material is easy to handle in the factory. Being applied in liquid form without heat it can be applied with great speed. As it becomes soft by mere addition of water, and without heat, there is neither danger nor expense for heating. As it dries with comparative rapidity, space required for handling a large quantity of stiffened sheet material, or articles such as shoes or hats in which it is embodied, is small.

Having thus described the general nature of the invention, an illustrative example of the manner of practicing the same will be given.

Thematerial preferred for the active ager of the-stiffener is sodium silicate having a relatively high ratio of silica to sodium, as

illustrated by the hypothetical formula ga ogsio p. This may be prepared by a own process. It maybe applied by any suitable method of spreading and impregna.-' tion. For example, 5 sheet of material such as felt, cloth or paper, may be run over a roller whose under rtion is immersed in a bath of the liqui sodium silicate. The liquid is brought up from the bath by the rotating roller as the sheet of felt is drawn over the roller. The liquid which is thus drawn up soaks into the felt. As the latter moves away, the surface of the sodium silicate which it has acquired loses water by evaporation and quickly becomes non-adhesive, which makes the coated sheet more easy to handle. Care should be taken that the skin of solidified articles resulting from the evaporation is su ciently formed before two treated layers of the sheet are placed in con- 5 tact with each other for storage else they will alhere together.

Where deep penetration of the sheet by the stifi'ener is not desired, the liquid stiffening material may be sprayed upon the surface of the sheet, either or both the sheet or the sprayer being in motion, the one relative to the other. Any suitable sprayin apparatus may be used for this purpose, as or example suc as works by a jet of compressed air, common- 1y called an atomizer, or one in which the fine subdivision of the liquid results from other characteristics of the jetting apparatus. In either case care should be taken that the superficial solidification of particles, due to evap- 1 oration of moisture which begins immediately upon issue of the finely sub-divided liquid particles from the nozzle, shall not proceed too far before they become settled on the material, for in that case the film on the sheet material will not have that continuous character which is desired, and which is attained, according to theinvention, by laying on the sheet a liquid film of the drying material and then drying that film so as to remove a part 1:0 of its associated water without destroying its film characteristic. I have found the hi her ratio silicates. and especially those haviiTT tlE ra :10 3 to J or of 4 to l to give greater strengti of film than solutions of lower ratio silicates wherein there is present the same amount of anhydrous material and the same percentage of water. In the case of an easy flowing solution of high ratio silicate which I have used, the original water content of the commercial product purchased for use in the process may be reduced markedly by evaporation, leaving a product which in that case contains approximatelyflipencent of water and which nevertheless is solid and free from 12 apparent moisture'jand the drying occurs with sufficient rapidity to make the material and method of treatment commercially valuable for stiffening the articles to which it is applied. If quicker solidification after ap- 10 COMPOSnmNS, W633 Reference tiiama'say COATING R PLASTIC.

plication is desired, more concentrated silithe last pulling, is effected by dustin on the cate solution may be a plied. I believe the surface of the moistened and complete y flexirapidity of drying to due in part to the ble box, just before lasting, a owdered salt fact that in these hi hratio silicates the molewhich Wlll take up water to orm a crystal 5 cules are organize in large hydrated units layer. The salt should be harmless and inof colloidal nature in which a considerable expensive and should in no stage of its appliportion of the water is held fast, and only a cation or use interfere with other processes portion is free to evaporate at ordinary temor the satisfactory use of the shoe. Such peratures; and that the extending of this salts are, particularly, sodium-sulphate and liquid in a film, or in globules when applied sodium-carbonate, both in the anhydrous conby spraying, produces such a large area of dition. These salts in the presence of the evaporative surface that whatever small part rightamount of water will take up water of water is free departs with great ease, quickand become crystalline; and in the rocess of ly forming the hard skin which, as evaporarapid stiffening of the silicate ox these 16 tion proceeds, rapidly extends from the surcrystals form a comparatively hard layer so face into and completely through the sheet over the surface of the box, which allows the or la er of stifl'ening material. last to be withdrawn promptly. Within a I have found that a satisfactory light half an hour or an hour however, the addiweight box toe can be made by laying the tional water in the silicate box will soften this above-described stiffening material directly crystal layer again, so that the hardening on the undersurface of the leather cap and effect is merely temporary; but by that time then proceeding through the lasting process evaporation will have proceeded to such a as usual. If the leather has been thus previpoint that the toe holds its shape. The temously impregnated and allowed to dry it may porary stiffening 1n this case is due to two he dipped in or painted with water or a suitactions: First the anhydrous salt withdraws 9o able softening solution, on the under side some water from the silicate, rendering it with water just prior to the lasting. If not stifier through that withdrawal of water; thus prepared it may be painted or sprayed, and, second, the anhydrous salt itself forms just prior to lasting, with the stiffening matea stiffening layer through its crystallization.

, rial in such concentration or such viscosity The acceleration to a permanent stiffening that it will stay on the surface rather than may be effected by similarly dusting, on the penetrate the fibers of the leather, and the surface of the moistened and flexible box, a lasting is then carried out as usual, producwhite insoluble oxide of an element that forms in a light but firm toe. an insoluble silicate. Such oxides are mag- Vhere the stiffener is to be protected from nesium oxide, zinc-oxide, aluminum oxide and water during subsequent use, it may be desircalcium oxide; the last isless desirable beable to la a waterproof layer a ainst-the cause of its recognized caustic qualities. In leather bef dre treating with the sti ening mathe case of these oxides reaction takes place terial, or to provide waterprooofing otherbetween the oxide and the silicate solution wise, as above described. Where it is deto form aderise, hard layer of insoluble silisired to combine in a toe the qualities of cate- T layer i permanent It is im- Strength d li ht weight, this can be done ggrtant' that the solidification of this layer and predetermined at will, according to the allowed to takeplace as much as possible needs of the case because .a wide latitude is free from disturban ,"-as otherwise the afi'orded, when the stiffener of the invention homogeneity of the layer-is destroyed. no is used, for choosing a suitable number and Th se mater als toproduce rapid stilfening variety of. layers in the composite box; or may be used w1th any of the .ordinary stiffenchoosing or varying the thickness of the supmg formulas elsewhere 'ment l ed herein.

porting medium, such as cloth, paper or felt AJI illustrative exam ie' of the practice (which latter especially may act as a carrier of h inVeIltIOIl would Q as follows, i1

for a eater or less thicknessof the stifi'ener mg a preferred procedure for application accor ing to the greater or less thickness of of the invention for certain purposes. Take the felt) or for applying the stiffener to the 3S g edlentst under surface of the toe cap; or varying the Solution of hi h-ratio silicate-to-soda alka concentration or amount of stifi'ener used in H Silicate solution, containing 15% of anliy the box. drous mattefr,200 parts, by weight;

Where it is desired to hasten the drying o Unboiled linse oil,7 parts, (boiled oil a silicate stiffener of the type hereinbefoi-e or varms may used);

described the stiffening may be a celerated, Gl cerine,9 parts.

5 so as tobequickly completed either ,emporari- If the particular qualities desired in the ly or permanently, so that in the case of a final product require it, the unboiled linseed shoe with box toe the last can be pulled withoil, boiled oil or varnish, may in part b 5f in a few minutes after being lasted. These cilac d liya emi'dr'iii or non-d inc fart two methods are as follows: oil. This an t e g ei-mm as The temporary stifi'ening, which permits property of projacing a degree of fiexibiljtvi.

(- I or a at in the silicate stifiened material; but when the oil is used a degree of water proofing is attained which is absent when glycerine alone is used.

An emulsion of these is applied to cloth sheeting, on one or more layers to the extent of from 300 to 1200 grams of mixed solution per square yard. The sheet is then air dried, and may later be dried with heat from steam.

\Vhen applied to sheet having a nap it may advantageously be applied on the nap side. In a typical case the material may be applied to one side of a sheet: then covered by a second sheet, and then, by application of pressure, made to penetrate the second sheet as well as the first. If the material is to be waterproofed by forming a layer of silica gel, the acid may be applied to one of the pieces of cloth by spraying it thereon. The emulsion having been worked into the body of the cloth the acid finds it there, and by reaction the acid entirely disappears, leaving the silica as one of the products of the chemical reaction that occurs in the body of the cloth. However, in a preferred arrangement, there is enough of silicate emulsion or solution to soak completely through both pieces of cloth to which it is applied; and in that case the acid when applied immediately meets the silicate and makes its deposit of silica on the outer surface of the composite sheet. For such an acid application of a solution of acetic acid preferably not stronger than 5 or 10% may be used. If waterproofing is to be accomplished by covering with a layer of waterproofing material, asphalt may be used, for which purpose the asphalt may be made of such temperature and viscosity that when laid on the surface it will form a layer and will not penetrate. The same general principle would cover the use of other waterproofing materials.

It is intended that the patent shall cover, by suitable expression in the appended claims,

whatever features of patentable novelty exist in the invention disclosed.

I claim as my invention:

1. A stifi'ened sheet of material which is flexible by nature and has disseminated through it a solidified soluble silicate and glycerin.

2. A stiffened sheet of material which is flexible by nature, said sheet being rendered stifi'er by havin associated with it a dried emulsionpf a silicate of an alkali metal With o1 stifi'ened sheet of material which is v flexible by nature, said sheet being rendered stifi'er by havin associated with it a dried emulsion of a si cate of an alkali metal with a drying oil.

4. A stifiened sheet of material which Is flexible by nature, said sheet being rendere I stiffer by iiavinlg associated with it a dried" ate of an alkali metal with a inixture of a and a non-drying fatty o1 5. A manufactured shape, such as a toe box,

made of sheet material which is flexible by.

nature and is rendered stifler by having associated with it a dried emulsion of a silicate of an alkali metal wherein the ratio of number of silica radicals to the number of alkali oxide radicals is three or more to one, and the oil is a drying oil.

6. A manufactured shape, such as a toe box, made of sheet material which is flexible by nature, rendered stifl'er by impregnation with an emulsion of a silicate of an alkali metal and oil.

7. A stiffened sheet of material which is flexible by nature, said sheet being rendered stiffer by having associated with it a dried emulsion of a silicate-05? an alkali metal with glycerine and a drying oil.

Signed at Boston, Massachusetts, this eleventh day of December, 1922.

WILLIS A. BOUGHTON. 

